The epothilones were first identified by Gerhard Hofle and colleagues at the National Biotechnology Research Institute as an antifungal activity extracted from the myxobacterium Sorangium cellulosum (see K. Gerth et al., 1996, J. Antibiotics 49:560-563 and Germany Patent No. DE 41 38 042). The epothilones were later found to have activity in a tubulin polymerization assay (see D. Bollag et al., 1995, Cancer Res. 55:2325-2333) to identify antitumor agents and have since been extensively studied as potential antitumor agents for the treatment of cancer.
The chemical structure of the epothilones produced by Sorangium cellulosum strain So ce 90 was described in Hofle et al., 1996, Epothilone A and B —novel 16-membered macrolides with cytotoxic activity: isolation, crystal structure, and conformation in solution, Angew. Chem. Int. Ed. Engl. 35(13/14): 1567-1569, incorporated herein by reference. The strain was found to produce two epothlone compounds, designated A (R═H) and B (R═CH3), as shown below, which showed broad cytotoxic activity against eukaryotic cells and noticeable activity and selectivity against breast and colon tumor cell lines. 
The desoxy counterparts of epothilones A and B. also known as epothilones C(R═H) and D (R═CH3), are known to be less cytotoxic, and the structures of these epothilones are shown below. 
Two other naturally occurring epothilones have been described. These are epothilones E and F, in which the methyl side chain of the thiazole moiety of epothilones A and B has been hydroxylated to yield epothilones E and F, respectively.
Because of the potential for use of the epothilones as anticancer agents, and because of the low levels of epothilone produced by the native So ce 90 strain, a number of research teams undertook the effort to synthesize the epothilones. This effort has been successful (see Balog et al., 1996, Total synthesis of (−)-epothilone A, Angew. Chem. Int.
Ed. Engl. 35(23/24): 2801-2803; Su et al., 1997, Total synthesis of (−)-epothilone B: an extension of the Suzuki coupling method and insights into structure-activity relationships of the epothilones, Angew. Chem. Int. Ed. Engl. 36(7): 757-759; Meng et al., 1997, Total syntheses of epothilones A and B. JACS 119(42): 10073-10092; and Balog et al., 1998, A novel aldol condensation with 2-methyl4-pentenal and its application to an improved total synthesis of epothilone B. Angew. Chem. Int. Ed. Engl. 37(19): 2675-2678, each of which is incorporated herein by reference). Despite the success of these efforts, the chemical synthesis of the epothilones is tedious, time-consuming, and expensive. Indeed, the methods have been characterized as impractical for the full-scale pharmaceutical development of an epothilone.
A number of epothilone derivatives, as well as epothilones A-D, have been studied in vitro and in vivo (see Su et al., 1997, Structure-activity relationships of the epothilones and the first in vivo comparison with paclitaxel, Angew. Chem. Int. Ed. Engl. 6(19): 2093-2096; and Chou et al., August 1998, Desoxyepothilone B: an efficacious microtubule-targeted antitumor agent with a promising in vivo profile relative to epothilone B, Proc. Natl. Acad. Sci. USA 95:9642-9647, each of which is incorporated herein by reference). Additional epothilone derivatives and methods for synthesizing epothilones and epothilone derivatives are described in PCT patent publication Nos. 99/54330, 99/54319, 99/54318, 99/43653, 99/43320,99/42602, 99/40047, 99/27890, 99/07692, 99/02514, 99/01124,98/25929, 98/22461, 98/08849, and 97/19086; U.S. Pat. No. 5,969,145; and Germany patent publication No. DE 41 38 042, each of which is incorporated herein by reference.
There remains a need for economical means to produce not only the naturally occurring epothilones but also the derivatives or precursors thereof, as well as new epothilone derivatives with improved properties. There remains a need for a host cell that produces epothilones or epothilone derivatives that is easier to manipulate and ferment than the natural producer Sorangium celfulosum. The present invention meets these and other needs.